CVE-2020-19726: GNU Binutils libbfd DoS Vulnerability

CVE-2020-19726 Overview

CVE-2020-19726 is a memory corruption vulnerability discovered in GNU Binutils libbfd.c version 2.36. The vulnerability relates to improper handling of auxiliary symbol data, which allows attackers to read or write to system memory or cause a denial of service condition. This flaw affects the core Binary File Descriptor (BFD) library that is fundamental to many GNU development tools.

Critical Impact
Attackers can exploit auxiliary symbol data processing to achieve arbitrary memory read/write capabilities or trigger denial of service, potentially compromising development environments and build systems.

Affected Products

GNU Binutils 2.36
Systems and tools using libbfd from affected versions
Development toolchains incorporating vulnerable binutils components

Discovery Timeline

2023-08-22 - CVE CVE-2020-19726 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-19726

Vulnerability Analysis

This vulnerability resides in the libbfd.c component of GNU Binutils, specifically in the processing of auxiliary symbol data within binary files. The Binary File Descriptor library is a critical component used by numerous GNU tools including objdump, readelf, nm, and the GNU linker (ld). When parsing specially crafted binary files containing malformed auxiliary symbol data, the library fails to properly validate memory boundaries, leading to out-of-bounds memory access conditions.

The vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption), indicating potential resource exhaustion scenarios. However, the ability to read from or write to arbitrary memory locations elevates this beyond a simple denial of service, potentially enabling information disclosure or code execution in certain scenarios.

Root Cause

The root cause stems from insufficient validation of auxiliary symbol data structures within libbfd.c. When processing object files, the BFD library parses symbol tables and their associated auxiliary data. The vulnerable code path fails to properly bounds-check array indices or buffer sizes when handling this auxiliary information, allowing crafted input to trigger out-of-bounds memory operations.

Attack Vector

The attack requires network-based delivery where a victim must interact with a maliciously crafted binary file. Typical attack scenarios include:

Convincing a developer to analyze a malicious object file using tools like objdump or readelf
Supplying poisoned library or object files to build systems
Compromising software repositories with malformed binaries
Embedding malicious binaries in seemingly legitimate software packages

The vulnerability requires user interaction—specifically, the victim must process the malicious file using a tool that relies on the vulnerable libbfd library. Exploitation does not require authentication or elevated privileges, as any user running affected binutils tools can trigger the vulnerability.

For detailed technical information about this vulnerability, see the Sourceware Bug Report #26240 and Sourceware Bug Report #26241.

Detection Methods for CVE-2020-19726

Indicators of Compromise

Unexpected crashes or segmentation faults in binutils tools (objdump, readelf, nm, ld)
Unusual memory consumption patterns during binary file processing
Core dumps generated by development tools with stack traces pointing to libbfd.c functions
Anomalous system memory access patterns during build processes

Detection Strategies

Monitor for abnormal termination signals (SIGSEGV, SIGBUS) from binutils processes
Implement file integrity monitoring for object files and libraries in development environments
Deploy application-level monitoring to track binutils tool execution patterns
Utilize SentinelOne Singularity Platform to detect memory corruption exploitation attempts in real-time

Monitoring Recommendations

Enable crash reporting and logging for all binutils tools in development and build environments
Implement network monitoring to detect suspicious binary file transfers to development systems
Establish baseline behavior for build systems and alert on deviations
Consider sandboxing binutils operations when processing untrusted binary files

How to Mitigate CVE-2020-19726

Immediate Actions Required

Update GNU Binutils to the latest patched version beyond 2.36
Audit systems for presence of vulnerable binutils version using ld --version or objdump --version
Restrict processing of binary files from untrusted sources
Implement sandboxing for development tools handling external binaries

Patch Information

GNU has addressed this vulnerability in subsequent releases of binutils. Organizations should update to the latest stable release of GNU Binutils. Detailed information about the patches can be found in the Sourceware bug tracking system:

Workarounds

Avoid processing untrusted binary files with vulnerable binutils versions
Run binutils tools in isolated containers or sandboxed environments when handling external files
Implement strict input validation for binary files entering build pipelines
Consider using alternative analysis tools until patching is complete

bash

# Check current binutils version
ld --version | head -n1

# Example: Update binutils on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade binutils

# Example: Update binutils on RHEL/CentOS systems
sudo yum update binutils